Normal growth depends upon rapid rates of protein accretion in premature and normal neonates. The highest rate of protein accretion are required in the most premature; clinically it continues to be difficult to achieve adequate protein in extremely premature newborns. Increase the protein synthesis and/ or reductions in proteolysis are necessary for effective protein accretion. In a series of studies we have demonstrated that intravenous nutrition is least effective in reducing whole body proteolysis in the most immature infants. The reason for this apparent resistance to suppressing proteolysis in extremely premature neonates remains unclear, and to what extent alteration in intravenous nutrition can better suppress proteolysis in this population is uncertain. Futhermore,nearly all previous studies in newborns have focused on whole body protein kinetics; how nutrition affects protein metabolism in specific tissues or organ beds remains unexplored. In particular, because the splanchnic organ bed in neonates represents a large fraction of body weight, is highly metabolically active, produces important proteins, and must process and/or deliver amino acids to peripheral organs, it is of special intrest to assess how nutrition influences splanchnic protein metabolism at different development stages. In the present application,we propose to test the overall hypothesis that the most immature neonates are the most sensitive to incomplete amino acid availability. Specifically, more complete intravenous amino acid solution are necessary to improve whole body protein anabolism, and an enteral amino acid supply is required to support splanchnic protein anabolism.